The title for No Such Thing as a Fish comes from a fact in the QI TV series. In the third episode of the eighth series, also known as "Series H", an episode on the theme of "Hoaxes" reported that after a lifetime studying fish, the biologist Stephen Jay Gould concluded that there was no such thing as a fish. He reasoned that although there are many sea creatures, most of them are not closely related to each other. For example, a salmon is more closely related to a camel than it is to a hagfish.[8] The opening of early episodes of the podcast used to feature a recording of the elves mentioning this fact, which appears in the first paragraph of the Oxford Encyclopedia of Underwater Life.[9][10]

https://en.m.wikipedia.org/wiki/No_Such_Thing_as_a_Fish#Title